This invention relates to a novel two-axis scanner. More specifically, it relates an optical scanner, driven by a single transducer, that scans a predetermined area.
Optical scanners are used in a variety of applications for the detection of information in a field of view. An important application is the sensing of data that has been imprinted on a surface in coded form, an example being the bar code imprinted on grocery store packages to identify the contents and the sources thereof. A typical scanner comprises a light source, a mirror positioned to reflect a beam of light from the source onto the field in which the data is to be sensed and an optical detector that responds to light reflected from the field of view. The mirror is mechanically connected to an electro-mechanical transducer that oscillates the mirror about a rotational axis and thereby causes the light beam to sweep back and forth so that the sensor repeatedly receives light reflected from a sequence of points along a line. The sensor thus provides an electrical signal corresponding with the imprinted data scanned by the light beam.
In some applications the light beam must be moved in two directions so as to scan an area instead of a single line. For example, it may be desirable to scan in a raster pattern comprising a series of substantially parallel lines. Alternatively, it may be desirable to scan along pairs of mutually orthoganal curves constituting a Lissajous pattern or similar configuration. A pattern of this latter type is useful in reading the aforementioned bar codes on packages, since it ensures that, by moving along a number of lines having different positions and orientations, the scanning beam will, during at least some of its sweeps, traverse all of the bars in the code despite the essentially random orientations of the bar codes with respect to the corresponding surface of the scanner.
Prior to the present invention, mechanical scanning along two axis has been accomplished primarily in two ways. In one system a beam is reflected from a mirror that rotates to move the beam along a first axis and is then reflected again from a second mirror that rotates in a plane orthogonal to the first plane. The twice-reflected beam thus moves in directions parallel to both planes and thereby scans an area in a field of view. In a sense the system comprises two complete single-axis scanners and thus is burdened with the cost and bulk of two scanners, together with the costs involved in aligning the scanners in a single optical system.
Another two-axis system employs a single mirror that is mounted on a first transducer for rotation in a first plane. The entire mirror-transducer assembly is mounted for rotation, in an orthogonal plane by a second transducer. The combined motion of the two transducers thus causes the mirror to rotate in both planes provide the desired area scanning function. Again the system is characterized by relatively high cost because of the need for two transducers, one of which must move the relatively large mass of the other transducer.